It is known to provide mass exchange packs in a column all around with rim guards which guide the liquid running down the inner column wall towards the mass exchange packings. The fastening of the rim guards is relatively problem-free when the mass exchange packing is circular at its periphery. But when the mass exchange pack has a corner on the outside, such as is the case when an inner separating wall is arranged, then a rim guard of rigid material is very hard to bend in the corner area.